Simulation of printed circuit board impedance variations and crosstalk effects

ABSTRACT

A method for altering an impedance of a conductive pathway on a microelectronic package includes applying a magnetic field to the conductive pathway. The microelectronic package may be, for example, a printed circuit board. The method also includes controlling a magnitude of the magnetic field at the conductive pathway for altering the impedance of the conductive pathway. The magnetic field may be applied by, for example, an electromagnet or a permanent magnet. A magnetic field may also be applied for simulating crosstalk effects on a conductive pathway.

BACKGROUND

1. Field of the Invention

The present invention relates to testing microelectronic packages, andmore specifically, to methods and systems of simulating impedancevariations and crosstalk effects during testing of printed circuitboards.

2. Description of Related Art

In many modern electronic systems, printed circuit boards and variousother microelectronic packages are used to connect electronic componentstogether for communication. A printed circuit board is typically a flatpanel that interconnects electronic components using a pattern of flatconductive pathways, often referred to as traces, which are formed on anon-conductive substrate. A printed circuit board may contain conductivepathway patterns on the top and bottom surfaces of the printed circuitboard or in layers through the interior of the printed circuit board.Conductive pathways on different layers of a printed circuit boardinterconnect through vias. Vias are conductive pathways that plate thewalls of holes extending through the layers of the printed circuitboard.

A single printed circuit board typically includes one or more conductivepathways between a transmitter and a receiver. A conductive pathway mayinclude one or more traces, vias, or combinations thereof connectedtogether for allowing electronic components, such as the transmitter andreceiver, to propagate signals to one another using electronicconduction. The transmitter and receiver may be mounted to the printedcircuit board and connected at designated portions of a trace pattern,often referred to as pads or lands. The transmitter and receiver may beconnected to the printed circuit board using, for example, surface mounttechnology, through-hole mounting technology, or any other suitabletechnology as known to those skilled in the art. Surface mounttechnology connects electronic components to a printed circuit board bysoldering electronic component leads or terminals to the top surface ofthe printed circuit board. Through-hole mount technology connectselectronic components to a printed circuit board by inserting componentleads through holes in the printed circuit board and then soldering theleads in place on the opposite side of the printed circuit board.

As printed circuit board data transmission speeds increase andtransmission signals include frequency components with wavelengthscomparable to the length of conductive pathways, it becomes necessary touse transmission line design techniques. The transition from lumpedelement behavior to transmission line behavior depends upon signal edgerates and on the total delay in the pulse transmission through aconductive pathway. In a lumped element mode, inductance and capacitanceappear to the pulse to be concentrated at a point within the printedcircuit board such that these factors do not need to be considered indesign. On the other hand, in a transmission line mode, inductance andcapacitance appear to be uniformly distributed throughout theinterconnection, and as far as the pulse is concerned, the conductivepathway is infinite in length, and all the characteristics of wavepropagation must be taken into consideration. Similar transmission linedesign techniques may be used for electrical characterization ofconductive pathways in all microelectronic packages. Basic transmissionline design parameters of interest include propagation delay,characteristic impedance, reflection coefficient, crosstalk, andrisetime degradation.

Field failure of printed circuit boards can arise from variationsbetween bulk-manufactured printed circuit boards and laboratory-testedprinted circuit boards. Variations causing field failure can be due, forexample, to the over-etch or under-etch of traces. As a result, theimpedance of a particular conductive pathway in a bulk-manufacturedprinted circuit board can vary significantly among severalbulk-manufactured printed circuit boards. For example, if the impedancevariation in a trace of a bulk-manufactured printed circuit board isabout 12%, a differential pair impedance having a nominal 100 ohmimpedance at nominal value could be expected to vary between about 88ohms and 112 ohms for testing purposes. When a printed circuit board isproduced in a laboratory, it is most often aligned towards nominalimpedance and has little manufacturing variation. Accordingly, there isa need for simple and accurate methods for simulating manufacturingvariations during laboratory testing. Particularly, there is a need forconvenient methods for simulating the impact of printed circuit boardimpedance variations within a laboratory environment.

Crosstalk is another transmission line parameter of interest to bevaried within a laboratory environment. Crosstalk is any phenomenon bywhich a signal transmitted on one conductive pathway or other sourcecreates an undesired effect in another conductive pathway. Accordingly,there is a need for convenient methods for simulating the effects ofcrosstalk on a conductive pathway of a printed circuit board duringtesting.

BRIEF SUMMARY

One or more embodiments of the present invention provide a method foraltering an impedance of a conductive pathway on a microelectronicpackage such as, but not limited to, a printed circuit board. The methodincludes applying a magnetic field to a conductive pathway on themicroelectronic package. Such a magnetic field may be applied by, forexample, but not limited to, an electromagnet or permanent magnet. Themethod includes controlling a magnitude of the magnetic field at theconductive pathway for altering the impedance of the conductive pathway.The magnitude of the magnetic field at the conductive pathway may becontrolled by, for example, but not limited to, selectively positioninga magnetic field generator with respect to the conductive pathway. Withrespect to use of an electromagnet, the magnitude of the magnetic fieldmay also be controlled by controlling the strength of current through acoil of the electromagnet.

One or more embodiments of the present invention provide a method forsimulating a range of possible manufacturing variations during testingof a microelectronic package such as, but not limited to, a printedcircuit board. The method includes using a magnetic field generator toapply a magnetic field to a conductive pathway on the microelectronicpackage. The method also includes measuring an impedance of theconductive pathway while the magnetic field is being applied to theconductive pathway. Further, the method includes calibrating themagnetic field generator based on the measured impedance. The methodalso includes using the magnetic field generator to control themagnitude of the magnetic field to alter the impedance of the conductivepathway to be within a predetermined impedance range. Further, themethod includes testing the microelectronic package while the impedanceof the conductive pathway is altered.

One or more embodiments of the present invention provide a method forsimulating effects of crosstalk on a conductive pathway of amicroelectronic package. The method includes applying a magnetic fieldto a conductive pathway on the microelectronic package. Further, themethod includes controlling a magnitude of the magnetic field at theconductive pathway for altering a crosstalk effect on the conductivepathway. A magnetic field generator as described herein may be used forapplying the magnetic field to the conductive pathway.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 sets forth a cross-sectional front plan view of a printed circuitboard and a magnetic field generator according to embodiments of thepresent invention.

FIG. 2 sets forth a top plan view of a printed circuit board and amagnetic field generator according to embodiments of the presentinvention.

FIG. 3 sets forth a cross-sectional front plan view of a printed circuitboard and a magnetic field generator according to embodiments of thepresent invention.

FIG. 4 sets forth a top plan view of a printed circuit board and amagnetic field generator according to embodiments of the presentinvention.

FIG. 5 sets forth a flow chart illustrating an exemplary method ofcalibrating a system and altering impedance of a conductive pathway in atesting environment according to embodiments of the present invention.

DETAILED DESCRIPTION

Exemplary methods and systems for simulating printed circuit boardimpedance variations and crosstalk effects in accordance withembodiments of the present invention are described herein. Particularly,described herein are exemplary methods and systems for simulatingbulk-manufactured printed circuit board impedance variations inaccordance with embodiments of the present invention are describedherein. In addition, exemplary methods and systems for simulatingcrosstalk effects in microelectronic packages in accordance withembodiments of the present invention are described herein.

It will be recognized by those skilled in the art that the methods andsystems described herein may also be similarly applied to simulation ofimpedance variations or crosstalk effects in any type of microelectronicpackage. Using the methods and systems described herein, researchers andengineers can conveniently simulate impedance variations or crosstalkeffects in a conductive pathway of a printed circuit board for testingof the printed circuit board. In this way, researchers and engineers canverify whether a printed circuit board having a particular design willsatisfactorily function if manufactured having the tested impedancevariations or crosstalk effects. By verifying that a printed circuitboard will operate within the tested impedance variations or crosstalkeffects, the likelihood of field failure can be significantly reduced.

As mentioned above, conductive pathways in printed circuit board andother microelectronic packages behave as transmission lines astransmission speeds increase and transmission signals include frequencycomponents with wavelengths comparable to the length of the conductivepathways. For the purpose of transmission line design, a transmissionline may be represented by the following components: resistance (R),inductance (L), capacitance (C), and conductance (G). By applyingKirchoff's voltage and current law, the following equations may be usedfor modeling a small length Δx of a conductive pathway:

${{v\left( {x,t} \right)} - {R\; \Delta \; {{xi}\left( {x,t} \right)}} - {L\; \Delta \; x\frac{\partial{i\left( {x,t} \right)}}{\partial t}} - {v\left( {{x + {\Delta \; x}},t} \right)}} = 0$${{i\left( {x,t} \right)} - {G\; \Delta \; {{xv}\left( {{x + {\Delta \; x}},t} \right)}} - {C\; \Delta \; x\frac{\partial{v\left( {{x + {\Delta \; x}},t} \right)}}{\partial t}} - {i\left( {{x + {\Delta \; x}},t} \right)}} = 0$

Solving the second order differential equation results in the followingequations for voltage and current waves, V(x) and I(x), respectively:

V(x) = V_(o)⁺^(−γ x) + V₀⁻^(+γ x)I(x) = I_(o)⁺^(−γ x) + I₀⁻^(+γ x), where${\gamma = {{\alpha + {j\beta}} = \sqrt{\left( {R + {{j\omega}\; L}} \right)\left( {G + {{j\omega}\; C}} \right)}}},{\alpha = {\frac{1}{2}\left( {{R\sqrt{\frac{C}{L}}} + {G\sqrt{\frac{L}{C}}}} \right)}},{and}$$\beta = {\omega {\sqrt{LC}.}}$

In these equations, γ is the complex propagation constant, α is theattenuation constant, and β is the propagation constant. Solving forimpedance provides the characteristic impedance of the transmission lineas provided in the following equations:

$\gamma = {{\alpha + {j\beta}} = \sqrt{\frac{R + {{j\omega}\; L}}{G + {{j\omega}\; C}}}}$

for a lossy transmission line; and

$Z_{0} = \sqrt{\frac{L}{C}}$

for a loss less transmission line.

In accordance with one or more embodiments of the present invention, amagnetic field can be applied to a conductive pathway on a printedcircuit board under testing for altering an impedance of the conductivepathway. The impedance of the conductive pathway can be altered toimpedances within a range that can be expected due to manufacturingvariations. FIG. 1 sets forth a system 100 for applying a magnetic fieldto a conductive pathway 102 on a printed circuit board 104, illustratedin cross-sectional front plan view, to alter an impedance of theconductive pathway 102 in accordance with embodiments of the presentinvention. The conductive pathway 102 extends between a transmitter 106and a receiver 108. FIG. 2 sets forth in top plan view the exemplaryprinted circuit board 104 and the system 100 illustrated in FIG. 1. Thetransmitter 106 and the receiver 108 of FIGS. 1 and 2 mount to thesurface of the printed circuit board 104 and connect to the printedcircuit board 104 at contact pads. The transmitter 106 and the receiver108 may be connected to the printed circuit board 104 using any suitabletechnology as understood by those skilled in the art. The conductivepathway 102 includes trace 110, via 112, trace 114, via 116, and trace118, and provides a path that allows the transmitter 106 to propagate atransmission signal to the receiver 108 by electrical conduction.

The printed circuit board 104 may be tested in a laboratory environmentusing laboratory test equipment 120 as understood by those skilled inthe art. For example, the printed circuit board 104 may be tested fordetecting the presence of hardware failures induced by faults in themanufacturing process or by operating stress or wearout mechanisms. Thebehavior of the digital system of the printed circuit board 104 may becharacterized by discrete responses to discrete operating state/inputsignal permutations such that testing of digital circuits may beachieved by checking their behavior under at least a portion of everyoperating mode and input signal permutation. The test equipment 120 mayapply tests to the printed circuit board 104 while impedance variations,crosstalk effects, or both are simulated on the printed circuit board104 as described herein in accordance with one or more embodiments ofthe present invention.

During testing of the printed circuit board 104, the system 100 includesa magnetic field generator 122 and a computing device 124 to simulatepotential manufacturing variations or adverse operational effects of theprinted circuit board 104 that could affect system performance. Themagnetic field generator 122 is communicatively coupled to the computingdevice 124 for receiving control signals from the computing device 124.Particularly, the computing device 124 communicates control signals tothe magnetic field generator 122 for controlling a magnitude of themagnetic field generated by the magnetic field generator 122. Byselectively positioning the magnetic field generator 122 in proximity tothe conductive pathway 102 of the printed circuit board 104 andcontrolling the magnitude of the magnetic field generated by themagnetic field generator 122, the magnitude of the magnetic fieldapplied to the conductive pathway 102 is controllable, and as a result,the impedance of the conductive pathway 102 is alterable. A researcheror engineer can thereby operate the computing device 124 to alter theimpedance of the conductive pathway 102 for simulating impedancevariations that could result from bulk-manufacturing processes or forsimulating crosstalk effects.

In this example, the magnetic field generator 122 includes a currentsource 126 and an electromagnet 128. The computing device 124 is coupledto the current source 126 and configured to communicate control signalsto the current source 126 for controlling the generation of electriccurrent by the current source 126. The current source 126 may generateelectric current and communicate the electric current through aconductive line 130 of the electromagnet 128. At least a portion of theconductive line 130 is wound in a coil, where several turns of theconductive line 130 are positioned side by side. When electric currentflows through the conductive line 130, the flow of current in the coilgenerates a magnetic field in the interior of the coil and in an areasurrounding the coil. The magnitude of the magnetic field is weaker atpositions further from the coil. Accordingly, the coil of theelectromagnet 128 may be selectively positioned with respect to theconductive pathway 102 for controlling the variance of the magnitude ofthe magnetic field applied to the conductive pathway 102. Therefore, theimpedance in the conductive pathway 102 can be varied based on theposition of the electromagnet 128 with respect to the conductive pathway102. As the electromagnet 128 is moved closer to the conductive pathway102, the impedance of the conductive pathway 102 increases. Conversely,as the electromagnet 128 is moved further from the conductive pathway102, the impedance of the conductive pathway 102 decreases. Accordingly,a researcher or engineer can selectively position the electromagnet 128with respect to the conductive pathway 102 to selectively alter theimpedance of the conductive pathway 102 for simulating impedancevariations that could result from bulk-manufacturing processes. Thepositioning of the electromagnet 128 with respect to a conductivepathway will vary depending on the strength of the magnetic fieldgenerated by the electromagnet 128, the physical topology of the printedcircuit board 104, and the desired alteration to the impedance of theconductive pathway 102.

The magnitude of the magnetic field applied to the conductive pathway102 may also be varied by controlling current passing through theconductive line 130 of the electromagnet 128. The computing device 124may control the current source 126 to output current through theconductive line 130 of the electromagnet 128 for generating a magneticfield. By increasing the strength of the current flow through theconductive line 130, the magnitude of the magnetic field generated bythe electromagnet 128 increases. Conversely, by decreasing the strengthof the current flow through the conductive line 130, the magnitude ofthe magnetic field generated by the electromagnet 128 decreases. Byincreasing the magnitude of the magnetic field at the conductive pathway102, the impedance of the conductive pathway 102 is increased.Conversely, by decreasing the magnitude of the magnetic field at theconductive pathway 102, the impedance of the conductive pathway 102 isdecreased. The computing device 124 can communicate control signals tothe current source 126 for varying the strength of the current flow andcan thus control the magnitude of the magnetic field for controlling theimpedance of the conductive pathway 102. The computing device 124 canalso control the current source 126 to stop the flow of current suchthat no magnetic field is generated by the electromagnet 128, therebythe impedance of the conductive pathway 102 is not altered. A researcheror engineer can input commands into the computing device 124 forcontrolling the magnitude of the magnetic field applied to theconductive pathway 102 to selectively alter the impedance of theconductive pathway 102 for simulating impedance variations that couldresult from bulk-manufacturing processes.

Impedance of a conductive pathway can be altered based on the magneticfield direction with respect to the direction of signal transmission.Particularly, for example, impedance of the conductive pathway 102 maybe increased by inducing a magnetic field in a direction opposing signaltransmission. For example, transmitter 106 may communicate electricalsignals to the receiver 108 using the conductive pathway 102 and in adirection generally designated by arrow 132. To increase impedance tothis signal transmission, the current source 126 communicates currentthrough the conductive line 130 such that the magnetic field generatedtherefrom generally opposes the transmission of electrical signalscommunicated from the transmitter 106 to the receiver 108.

Conversely, to decrease impedance to signal transmission in the generaldirection of arrow 132, another current source 134 and electromagnet 136having a coiled conductive line 138 may be oriented to produce amagnetic field that is generally in a direction that is the same as thesignal transmission. The resulting magnetic field thereby causes adecrease in the impedance of the conductive pathway 102. Alternatively,the current source 134 and electromagnet 134, or any other magneticfield generator described herein, may be applied to a conductive pathwayon the printed circuit board 104 that is different than the conductivepathway 102. Any number of magnetic field generators may be used whiletesting a printed circuit board in accordance with embodiments of thepresent invention for simulating impedance variation ranges on one ormore conductive pathways of the printed circuit board.

The computing device 124 may include a computer, which may include oneor more computer readable medium(s). The computer may include suitablehardware, such as a processor, and software (including firmware,resident software, micro-code, etc.) for interfacing with andcontrolling the current sources 126 and 134 to vary the current appliedto the coils of the electromagnets 128 and 136, respectively. Inaddition, the computer may include a suitable user interface (e.g., akeyboard, a display, a mouse, etc.) for allowing an operator to inputcommands for controlling the current sources 126 and 134.

In another embodiment of the present invention, a permanent magnet maybe used in place of the electromagnet and computing device shown inFIGS. 1 and 2 for altering impedance of a conductive pathway. FIGS. 3and 4 illustrate a system using a permanent magnet as a magnetic fieldgenerator for generating a magnetic field for altering impedance of aconductive pathway. With reference now to FIGS. 3 and 4, the printedcircuit board 104 is the same as the printed circuit board 104 of FIGS.1 and 2. In this example, a permanent magnet 300 generates a magneticfield at the conductive pathway 114 for altering the impedance of theconductive pathway 114. The permanent magnet 300 may be used in place ofor together with the magnetic field generator 122 and the computingdevice 124 for generating a magnetic field to alter the impedance of theconductive pathway 114. The permanent magnet 300 may be any suitableobject made from a material that is magnetized and creates its ownpersistent magnetic field.

The permanent magnet 300 may be selectively positioned with respect tothe conductive pathway 102 for altering impedance of the conductivepathway 102. The closer the permanent magnet 300 is positioned to theconductive pathway 102, the higher the impedance of the conductivepathway 102. Conversely, the further the permanent magnet 300 ispositioned from the conductive pathway 102, the lower the impedance ofthe conductive pathway 102. The positioning of the permanent magnet 300with respect to the conductive pathway 102 will vary depending on thestrength of the magnetic field generated by the permanent magnet 300,the physical topology of the printed circuit board 104, and the desiredalteration to the impedance of the conductive pathway 102.

The strength and orientation of the permanent magnet 300 also affectsalteration of the impedance of the conductive pathway 102. With respectto the permanent magnet's 300 strength, the higher its strength, thegreater the effect on the strength of the conductive pathway 102. Withrespect to the orientation of the permanent magnet 300, the placement ofthe north and south ends of the permanent magnet 300 may be switched forchanging the direction of the magnetic field with respect to signaltransmission. As discussed above, to increase impedance to a signaltransmitted from the transmitter 106 to the receiver 108, the permanentmagnet's poles can be positioned as shown in FIGS. 3 and 4 such that themagnetic field generated therefrom generally opposes the transmission ofelectrical signals communicated from the transmitter 106 to the receiver108. Conversely, to decrease impedance to signal transmission in thegeneral direction of arrow 132, the permanent magnet 300 may be movedsuch that the poles N and S are switched, and as a result, the magneticfield causes a decrease in the impedance of the conductive pathway 102.

In the examples provided herein, systems and methods are described formagnetic field generation for altering a single conductive pathway on aprinted circuit board. However, one of ordinary skill in the art willunderstand that a magnetic field generated in accordance withembodiments of the present invention may be applied to more than oneconductive pathway on a printed circuit board. Further, a magnetic fieldgenerated in accordance with embodiments of the present invention may beapplied to a conductive pathway on any type of microelectronic package.

It should also be noted that although more than one electromagnet isshown in FIGS. 1 and 2 and only one permanent magnet is shown in FIGS. 3and 4, such component numbers are not a requirement or limitation forthe present invention. Rather, any suitable number of electromagnets,permanent magnets, or combinations thereof may be used for generatingmagnetic fields for affecting the impedance of a conductive pathway on amicroelectronic package. The number of such magnetic field generatorsthat alter the impedance of conductive pathway(s) can vary from onemicroelectronic package topology to another depending on the physicaltopology of the microelectronic package and the desired alteration tothe impedance of the conductive pathway(s).

As mentioned above, excessive crosstalk in conductive pathways ofprinted circuit boards can adversely affect system performance. Themethods and systems described herein in accordance with embodiments ofthe present invention may be utilized for simulating crosstalk effectson one or more conductive pathways of a printed circuit board or othermicroelectronic package. An exemplary method according to embodiments ofthe present invention includes applying a magnetic field to a conductivepathway on a microelectronic package. For example, the magnetic fieldsapplied to the conductive pathway 102 described with respect to FIGS.1-4 may be applied to the conductive pathway 102 for simulatingcrosstalk effects. Now referring to FIGS. 1-4, the exemplary method alsoincludes controlling a magnitude of the magnetic field at the conductivepathway 102 as described herein with respect to embodiments of thepresent invention. The magnitude of the magnetic field at the conductivepathway 102 may be controlled for altering crosstalk effect on theconductive pathway 102. The strength of the magnet field applied to theconductive pathway 102 may be varied over time for simulating crosstalkeffects. While the crosstalk effects are simulated, the test equipment120 may apply tests to the printed circuit board 104. Accordingly, aresearcher or engineer may test the printed circuit board 104 whilecontrolling simulation of crosstalk effects.

As referred to herein, a magnetic field generator may be any componentor device capable of generating a magnetic field. For example, amagnetic field generator may be a permanent magnet made of, but notlimited to, a magnetically hard ferromagnetic material that remainsmagnetized. In another example, a magnetic field generator may includean electromagnet, the strength of which can be controlled by currentoutput from any suitable current source. As mentioned above, anelectromagnet may be made from a coil of wire which acts as a magnetwhen an electric current passes through it, but stops when the currentstops. The coil of the electromagnet may be wrapped around a core offerromagnetic material, such as, for example, a core of ferromagneticmaterial like steel, which enhances the magnetic field produced by thecoil.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.), or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module,” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium (including, but not limitedto, non-transitory computer readable storage media). A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the lattersituation scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus, or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

As mentioned above, exemplary methods for applying a magnetic field to aconductive pathway on a microelectronic package for controlling animpedance of the conductive pathway in accordance with embodiments ofthe present invention are described with reference to the accompanyingdrawings. The impedance of the conductive pathway may be altered withina predetermined impedance range to simulate bulk-manufacture variationsin a testing environment. Prior to its use in testing a microelectronicpackage, a system according to embodiments of the present invention maybe calibrated to the microelectronic package. For further explanation,FIG. 5 sets forth a flow chart illustrating an exemplary method ofcalibrating a system and altering impedance of a conductive pathway in atesting environment according to embodiments of the present invention.The method of FIG. 5 includes measuring 500 an impedance of a conductivepathway on a printed circuit board that may be produced in a laboratory.For example, a time-domain reflectometer may be used for measuring animpedance of the conductive pathway 102 on the printed circuit board 104shown in FIGS. 1 and 2. In this example, the conductive pathway 102 maybe measured at a nominal 100 ohm impedance. A laboratory researcher orengineer may determine to test the printed circuit board 104 at animpedance variation range of ±12%, for example, from the nominalimpedance value. The laboratory researcher or engineer may thencalibrate a system as described herein below for generating and varyinga magnetic field for altering the impedance of the conductive pathway102 at ±12% from the nominal impedance value. This impedance variationmay be deemed to be the possible variation from the actual design in aprinted circuit board produced by bulk-manufacturing. Any suitableimpedance variation range may be applied to a printed circuit board orother microelectronic package for testing by a laboratory researcher orengineer.

To calibrate a system according to embodiments of the present invention,the method of FIG. 5 includes applying 502 a magnetic field to theconductive pathway on the printed circuit board using a magnetic fieldgenerator. The magnetic field can be varied as described herein foraltering the magnitude of the magnetic field applied to the conductivepathway, thereby the impedance of the conductive pathway is also varied.As the impedance of the conductive pathway is varied, the control of themagnetic field generator for achieving a range of impedance values forthe conductive pathway can be known by measuring the impedance with atime-domain reflectometer as the magnetic field is varied. In this way,the magnetic field generator is calibrated because the laboratoryresearcher or engineer can know the control inputs needed for varyingthe magnetic field to achieve a desired impedance range. In theexemplary system 100 of FIGS. 1 and 2, the positioning and/or currentinput into the electromagnet 128 can be varied for determining thepositioning and/or control of the current needed for achieving a desiredimpedance range for conductive pathway 102. In the exemplary system ofFIGS. 3 and 4, the permanent magnet 300 may be moved to differentpositions for determining the positioning needed for achieving a desiredimpedance range for conductive pathway 102.

After calibration of a system according to embodiments of the presentinvention, the method of FIG. 5 includes applying 504 a magnetic fieldto the conductive pathway to alter the impedance of the conductivepathway to a value within a range desired for testing the printedcircuit board. For example, the laboratory researcher or engineer canknow the control input needed for achieving a desired impedance valuefor testing the printed circuit board 104. The magnetic field generator(e.g., the electromagnet magnet 128 or permanent magnet 300) may becontrolled to apply a magnetic field to the conductive pathway 102 forachieving the desired impedance value.

Next, the method of FIG. 5 includes applying 506 tests to the printedcircuit board while the impedance of the conductive pathway is alteredto be within the predetermined impedance range. For example, thelaboratory researcher or engineer may apply tests to the printed circuitboard 104 while the magnetic field generator is controlled to apply amagnetic field to the conductive pathway 102 for achieving the desiredimpedance value. The magnetic field may be held at that value untiltesting is complete, or the magnetic field may be altered to vary theimpedance of the conductive pathway over a range while the printedcircuit board is tested. As a result, the laboratory researcher orengineer may simulate impedance variations in a conductive pathway of aprinted circuit board for testing of the printed circuit board. Theseare the impedance variations that may be expected to result inbulk-manufacturing of the printed circuit board.

In view of the explanations set forth above, readers will recognize thatthe benefits of the systems and methods according to embodiments of thepresent invention for simulating bulk-manufactured, printed circuitboard impedance variations during testing include: simpler and moreaccurate methods for simulating manufacturing variations duringlaboratory testing; and reducing the likelihood of field failures inbulk-manufactured, printed circuit boards.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be noted,in some alternative implementations, the functions noted in the blockmay occur out of the order noted in the Figures. For example, two blocksshown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method comprising: applying a magnetic field to a conductivepathway on a microelectronic package; and controlling a magnitude of themagnetic field at the conductive pathway for altering an impedance ofthe conductive pathway.
 2. The method of claim 1, wherein themicroelectronic package is a printed circuit board.
 3. The method ofclaim 1, wherein applying a magnetic field comprises using anelectromagnet to apply the magnetic field to the conductive pathway. 4.The method of claim 3, wherein controlling a magnitude of the magneticfield comprises moving the electromagnet with respect to the conductivepathway.
 5. The method of claim 3, wherein controlling a magnitude ofthe magnetic field comprises controlling electric current passingthrough the electromagnet.
 6. The method of claim 1, wherein applying amagnetic field comprises using a permanent magnet to apply the magneticfield to the conductive pathway.
 7. The method of claim 6, whereincontrolling a magnitude of the magnetic field comprises moving thepermanent magnet with respect to the conductive pathway.
 8. The methodof claim 1, wherein controlling a magnitude of the magnetic fieldcomprises controlling the magnitude of the magnetic field to one ofincrease and decrease the impedance of the conductive pathway to bewithin a predetermined impedance range, and wherein the method furthercomprises testing the microelectronic package while the impedance of theconductive pathway is altered.
 9. A method comprising: using a magneticfield generator to apply a magnetic field to a conductive pathway on amicroelectronic package; measuring an impedance of the conductivepathway while the magnetic field is being applied to the conductivepathway; calibrating the magnetic field generator based on the measuredimpedance; using the magnetic field generator to control the magnitudeof the magnetic field to alter the impedance of the conductive pathwayto be within a predetermined impedance range; and testing themicroelectronic package while the impedance of the conductive pathway isaltered.
 10. The method of claim 9, wherein the microelectronic packageis a printed circuit board.
 11. The method of claim 9, wherein themagnetic field generator comprises: an electromagnet; and a computingdevice coupled to the electromagnet and configured to control amagnitude of electric current passing through the electromagnet forcontrolling the magnitude of the magnetic field at the conductivepathway.
 12. A method comprising: applying a magnetic field to aconductive pathway on a microelectronic package; and controlling amagnitude of the magnetic field at the conductive pathway for altering acrosstalk effect on the conductive pathway.
 13. The method of claim 12,wherein the microelectronic package is a printed circuit board.
 14. Themethod of claim 12, wherein applying a magnetic field comprises using anelectromagnet to apply the magnetic field to the conductive pathway. 15.The method of claim 12, wherein applying a magnetic field comprisesusing a permanent magnet to apply the magnetic field to the conductivepathway.
 16. A system comprising: a microelectronic package including aconductive pathway; test equipment coupled to the microelectronicpackage for testing the microelectronic package; and a magnetic fieldgenerator positioned in proximity to the conductive pathway andconfigured to apply a magnetic field to the conductive pathway such thatthe magnetic field alters an impedance and crosstalk of the conductivepathway for simulating impedance variations while the microelectronicpackage is under testing.
 17. The system of claim 16, wherein themicroelectronic package is a printed circuit board.
 18. The system ofclaim 16, wherein the magnetic field generator is a permanent magnet.19. The system of claim 16, wherein the magnetic field generatorincludes an electromagnet and a computing device.
 20. The system ofclaim 19, wherein the computing device is configured to control electriccurrent passing through the electromagnet.
 21. The system of claim 19,wherein the computing device is configured to control the magnitude ofthe magnetic field such that the impedance of the conductive pathway isaltered to an impedance within a predetermined impedance range, andwherein the computing device is configured to control the electromagnetto maintain the impedance within the predetermined impedance range whilethe testing equipment tests the microelectronic package.
 22. The systemof claim 19, wherein the magnetic field generator includes anotherelectromagnet coupled to the computing device for control of the otherelectromagnet by the computing device.
 23. The system of claim 16,further comprising a computing device calibrated based on a measuredimpedance of the conductive pathway while the magnetic field generatorapplies the magnetic field to the conductive pathway, and wherein thecomputing device is configured to control the magnitude of the magneticfield such that the impedance of the conductive pathway is altered to animpedance within a predetermined impedance range.
 24. The system ofclaim 23, wherein the magnetic field generator includes anelectromagnet, and wherein the computing device is coupled to theelectromagnet and configured to control a magnitude of electric currentpassing through the electromagnet for controlling the magnitude of themagnetic field applied at the conductive pathway.
 25. The system ofclaim 23, further comprising an electronic meter coupled to themicroelectronic package and configured to measure an impedance of theconductive pathway while the magnetic field is being applied to theconductive pathway for determining the measured impedance.